1. Field of the Invention
The present invention relates to a friction material, particularly relates to a friction material for use in an industrial machine, a railway vehicle, a baggage car, a passenger car, or the like, and more particularly relates to a friction material in a brake pad, a brake lining, a clutch facing, or the like, for use in the above-mentioned applications.
2. Description of the Related Art
In a friction material to be used mainly in a brake pad or the like, a fibrous reinforcement is used as one of materials for enhancing the strength of the friction material. Fibrous reinforcements used in place of asbestos fiber include rock wool, slag wool, Al2O3xe2x80x94SiO2-type ceramics fiber, which includes Al2O3xe2x80x94SiO2 as a main component, glass fiber, steel fiber, Aramid fiber, potassium titanate fiber, etc. Since these fibrous reinforcements have their own properties, a mixture of several kinds of them is used.
Among these fibrous reinforcements, rock wool using a natural ore as the raw material, slag wool using slag in steelmaking as the raw material and having the same composition as rock wool, and Al2O3xe2x80x94SiO2-type ceramics fiber are rated highly, as abrasive hard inorganic fiber, in the point that not only can they improve the strength, the heat resistance and the abrasion resistance of the friction material as a whole, but also they can enhance a friction coefficient of the friction material through their abrasive properties, and particularly they can ensure a high friction coefficient at the time of a high load such as high-speed braking or the like.
Rock wool, slag wool and Al2O3xe2x80x94SiO2-type ceramics fiber which have been used in place of asbestos fiber are low in price and easily available. However, since they have a fibrous form, their use tends to be regulated on working-environmental hygiene.
It is an object of the present invention to provide a friction material in such a manner that, when inorganic fiber is used as fibrous reinforcements, any fibrous reinforcements of rock wool, slag wool and Al2O3xe2x80x94SiO2-type ceramics which have a tendency that the use of them may be regulated in future are not used, nevertheless a friction effect equal to that in the case of using those fibrous reinforcements can be provided.
In order to solve the foregoing problem, the present inventors carried out various researches about materials and forms of inorganic substances using no fibrous reinforcements of rock wool, slag wool and Al2O3xe2x80x94SiO2-type ceramics having a tendency to be regulated in use, but nevertheless giving a friction material a friction effect equal to that in the case of using those fibrous reinforcements. As a result, the inventors found that the fibrous form of the fibrous reinforcements of rock wool, slag wool and Al2O3xe2x80x94SiO2-type ceramics was a primary factor in their problem on working-environmental hygiene.
The present invention was attained taking it into consideration that, when rock wool, slag wool and Al2O3xe2x80x94SiO2-type ceramics were used in particulate forms, it was possible to obtain a friction effect equal to that in the case using them as fibrous reinforcements.
That is, the present invention solved the foregoing problem as described below.
There is provided a friction material composed of a fibrous reinforcement, a friction modifier and a binder, wherein fibrous reinforcements of rock wool, slag wool and Al2O3xe2x80x94SiO2-type ceramics are not contained, and non-fibrous particulate matter having the same material as any one of the fibrous reinforcements is mixed as an abrasive component.
Preferably, in the above-mentioned friction material according to the present invention, the non-fibrous particulate matter is shot or crushed matter.
It is more preferable that, in the above-mentioned friction material according to the present invention, the particulate matter is subjected to surface treatment with a silane coupling agent, phenol resin, or the like.
Moreover, in the above-mentioned friction material according to the present invention, preferably, the particulate matter is mixed at a ratio in the range of 0.5 wt % to 20 wt % of the whole of the friction material.
It is more preferable that, in the above-mentioned friction material according to the present invention, the particulate matter is mixed at a ratio in a range of from 1 wt % to 15 wt % of the whole of the friction material.
Moreover, in the above-mentioned friction material according to the present invention, preferably, the diameter of the particulate matter is in the range of from 2 xcexcm to 100 xcexcm.
It is more preferable that, in the above-mentioned friction material according to the present invention, the diameter of the particulate matter is in the range of 2 xcexcm to 50 xcexcm.